The use of high-performance composite fiber materials is becoming increasingly common in applications such as aerospace and aircraft structural components. As is known to those familiar with the art, fiber reinforced composites consist of a reinforcing fiber such as carbon or KEVLAR and a surrounding matrix of epoxy, PEEK or the like. Most of the composite materials are formed by laminating several layers of textile fabric, by filament winding, or by cross-laying of tapes of continuous filament fibers. However, all of the structures tend to suffer from a tendency toward delamination. Thus, efforts have been made to develop three-dimensional braided, woven and knitted preforms as a solution to the delamination problems inherent in laminated composite structures.
For example, U.S. Pat. No. 3,834,424 to Fukuta et al. discloses a three-dimensional woven fabric as well as method and apparatus for manufacture thereof. The Fukuta et al. fabric is constructed by inserting a number of double filling yarns between the layers of warp yarns and then inserting vertical yarns between the rows of warp yarns perpendicularly to the filling and warp yarn directions. The resulting construction is packed together using a reed and is similar to traditional weaving with the distinction being that "filling" yarns are added in both the filling and vertical directions. Fukuta et al. essentially discloses a three-dimensional orthogonal woven fabric wherein all three yarn systems are mutually perpendicular, but it does not disclose or describe any three-dimensional woven fabric having a configuration other than a rectangular cross-sectional shape. This is a severe limitation of Fukuta et al. since the ability to form a three-dimensional orthogonal weave with differently shaped cross sections (such as , , , and ) is very important to the formation of preforms for fibrous composite materials. Applicants have overcome this shortcoming of Fukuta et al. by providing a three-dimensional weaving method which provides for differential weft insertion from both sides of the fabric formation zone so as to allow for an unexpectedly and surprisingly superior capability of producing three-dimensional fabric constructions of substantially any desired cross-sectional configuration.
Also of interest, Fukuta et al. U.S. Pat. No. 4,615,256 discloses a method of forming three-dimensionally latticed flexible structures by rotating carriers around one component yarn with the remaining two component yarns held on bobbins supported in the arms of the carriers and successively transferring the bobbins or yarn ends to the arms of subsequent carriers. In this fashion, the two component yarns transferred by the carrier arms are suitably displaced and zig-zagged relative to the remaining component yarn so as to facilitate the selection of weaving patterns to form the fabric in the shape of cubes, hollow angular columns, and cylinders.
Another type of orthogonally woven reinforcing structure is disclosed by U.S. Pat. No. 3,993,817 to Schultz et al. The apparatus disclosed by Schultz et al. fabricates a woven structure from axial, radial, and circumferential sets of threads. The radial threads are drawn from bobbins and passed through aligned thread guides in successive disks which are arranged about a common central axis and slightly spaced from each other axially. A circumferential thread is drawn from a bobbin and passed in a loop between each of two disks outside of the radial threads, and several turns of it are thus wrapped and the loop tightened to draw the radial threads inwardly. When the desired number of circumferential threads in a given layer have been wrapped between each pair of disks, axial threads are then threaded between adjacent radial threads by leading them through with a knitting needle, and further wraps of circumferential threads may be applied. In this particular orthogonal structure, the axial threads are straight and axially extending while the radial threads lie partly normal to and partly parallel to the axial threads. The circumferential threads are wrapped normal to the axial threads and in an interlaced relationship between and around the radial threads and upon and beneath the axial threads.
Other known methods for forming three-dimensional structures include the AUTOWEAVE BR900 and BR2000 systems developed by Brochier in France and installed at Avco Specialty Materials/Textron facility in Lowell, Mass. The computerized process entails inserting radial rods into a foam mandrel machined to conform to the inside shape of the final product and forming helical tapered corridors therein. Axial yarns are fed into the axial corridors by a shuttle and circumferential yarns are wound into the circumferential corridors to anchor the previously positioned axial yarns so that the alternating axial yarn and circumferential yarn placement produces layers which are used to build up the preformed wall thickness. U.S. Pat. No. 4,001,478 to King discloses yet another method to form a three-dimensional structure wherein the structure has a rectangular cross-sectional configuration as well as a method of producing cylindrical three-dimensional shapes.